1. Field of the Invention
This invention relates to energy converters, and more particularly to apparatus that transform electrical energy into mechanical energy or vice versa by way of magnetic energy. The energy converters according to this invention are used, for example, as linear motion actuators of voice coil motors.
2. Description of the Prior Art
An electric motor and an electric generator comprise a field magnet and an armature, with a permanent magnet or an electromagnet used as the field magnet. While small direct-current motors with brushes, brushless motors and synchronous motors extensively use permanent magnets, induction motors use electromagnets. Electric current is generally supplied to the movable part directly from a supply circuit. With induction motors, by contrast, electric current is induced to the armature by electromagnetic induction.
Recently, faster response, larger output and smaller size are required of motors and generators. Response time can be improved by either alleviating the load on the movable part or applying suitable control. If the load is great, however, improvement by control cannot be achieved because of the limit of power supply voltage. If the demand for quick response is acute, accordingly, reduction of the toad is an indispensable prerequisite. This is the reason why the weight reduction of the movable part is essential. For this reason, many coreless and voice coil motors dispense with the magnetic core or coil bobbin, with their movable part consisting of the armature's winding alone.
Measures to attain larger output and smaller size include the use of high-energy magnets made of rare earth elements and the reduction of the gap between the movable and stationary parts by increasing the accuracy of working and assembling. Coreless and voice coil motors, for example, use armature cells wound with high accuracy. Another measure to achieve output increase and size reduction comprises the use of lead wire coated with heat-resisting insulating material and heat-resisting adhesives to permit passing more current through the coils.
Despite these improvements, however, conventional motors and generators have been unable to fully satisfy the needs for faster response, larger output and smaller size as many problems are involved in the weight reduction of their movable part, improvement in the dimensional accuracy of windings, and enhancement of the heat resistance of coil insulators and adhesives. In particular, lightweight windings possessing both great dimensional accuracy and high heat resistance are difficult to obtain.